With some materials, the toughness varies, meaning you can use the lower-strength materials at lower temperatures. Availability, cost, forming could enter in as well.
In many cases there is a price premium for the higher strength grades. If your design will not allow you to make parts thin enough (for example stiffness limits) to take advantage of the strength and offset the cost, then it would be a waste.
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Rust never sleeps
Neither should your protection